In recent years, the oceans have begun to be tapped as sources of extractable thermal energy. The abundance of water at varying temperatures has been utilized in a number of systems as a heat transfer agent.
It has been proposed to utilize the ocean thermal energy in a Rankine cycle process to generate electrical energy. One such proposal, by the Lockheed Corporation, comprises pumping water through pipes for cooling the refrigerant which performs the work. Vast amounts of water are required to be pumped, requiring massive pumps which have not yet been designed and successfully manufactured. Maintenance and repair of such tremendous pumps would require huge handling equipment and greatly increase the cost of the system.
The pipes which would be utilized in such a system, if made of steel or other heavy, corrosion resistant, high strength metal, would be very heavy due to the wall thickness required to keep pipe deflections, caused by thermal differences and ocean currents, at a manageable level. This would then necessitate the use of large buoyancy tanks to keep the unit afloat. Such tanks would need variable buoyancy control which would consume some of the power generated by the system.
A particular disadvantage of this sort of system is the problem of biofouling and other marine environmental problems. Fish and plant life can be pumped into the system along with the ocean water, as well as ocean sediments which cause corrosion.
In mini-OTEC tests (Ocean Thermal Energy Conversion testing done on floating ships), a 50 KW output has been produced. Of this output, it is estimated that 45 KW was needed to operate the equipment, leaving only 5 KW available for transmission. Thus, to make a 300 mega-watt delivery OTEC, such as proposed by Lockheed, would require a unit capable of developing 3000 mega-watts.